Transplantation of human umbilical cord stem cells (hUCBC) has been shown to be effective in limiting infarct size and in the preservation of left ventricular function and anatomy in a rat model. These effects have been present in studies both utilizing and not utilizing immunosuppression. Whether immunosuppression will be required in a large animal model is unknown, as is the efficacy of transplantation of hUCBC in a large animal model. This data is critical in order to determine the risk:benefit ratio of this therapy, especially if immunosuppression is required; and in order to move this therapy into human clinical trials for the treatment of myocardial infarction and prevention of congestive heart failure which affects over 5 million patients in the U.S. This study is specifically designed to evaluate the effects of hUCBC transplantation following myocardial infarction on left ventricular function and anatomy and determine the necessity of immunosuppression in a porcine model. Forty-two animals will be studied; 6 animals will serve as controls (no myocardial infarction) and 36 animals will undergo myocardial infarction (MI). The MI group will consist of three (12 animals each) different treatment modalities (Group 1-no treatment, Group 2-treatment with Isolyte media injection into the infarct border zone, and Group 3-treatment with hUCBC injection into the infarct zone). Six animals in each treatment group will receive immunosuppression and six will receive no immunosuppression. Those animals that are designated for immunosuppression will receive cyclosporine 10 mg/kg twenty-four hours preoperatively and every day subsequently until sacrificed. The randomization will be blinded to pathologists, sonographers, and echocardiogram interpreters. LV function will be evaluated by echocardiography and invasive monitoring at 1, 2, and 4 wks and 2, 3, and 4 months. Animals will be sacrificed following evaluation and the heart tissue will be analyzed for infarct size, hUCBC engraftment, immunorejection, cardiac phenotype (using immunohistochemistry), and stem-cell derived endothelial cells. It is anticipated that the results from this study will assist in planning further studies for determination of the appropriate dosage, route, and timing of administration of hUCBC for the treatment of acute myocardial infraction to preserve left ventricular function and anatomy and prevent the development of congestive heart failure. [unreadable] [unreadable] [unreadable]